1. Technical Field
The present invention relates generally to drilling tools, and more particularly to the making of a drilling or abrading tool having a working surface with an array of blind apertures plugged with super-abrasive material.
2. Description of Related Art
Diamond-impregnated drill bits are well known to those skilled in the art. Such bits are conventionally manufactured using a powder metallurgy process wherein abrasive particles are randomly mixed within a matrix powder that is subjected to infiltration with a molten binder material. For example, diamond particles or grit may be mixed with a tungsten carbide powder, with the mixture then infiltrated by a molten copper alloy. Fusing of the tungsten carbide powder to retain the randomly distributed diamonds in alternative implementations may be effectuated by a hot isostatic pressing or sintering process.
The powder metallurgy process for diamond impregnation may be applied in connection with the making of the entire drill bit or parts of the drill bit. Alternatively, the powder metallurgy process for diamond impregnation may be applied in connection with the making of an impregnated construct or segment that is attached to a bit body so as to form the drill bit. Examples of such constructs include cells, blades or inserts affixed to the bit body by, for example, a brazing process.
There exist a number of concerns with respect to the prior art impregnated-diamond process and resulting impregnated-diamond drill bits.
First, the random distribution of grit or small carat weight diamond granules within a cell of tungsten carbide powder does not ensure smooth diamond coverage in the fused diamond-impregnated structure. Indeed, the random distribution necessarily implies an irregular diamond distribution including areas with diamond clusters, areas of lower diamond concentration, and even areas that are void of diamond content. As a result, the behavior of the cuttings across the impregnated working surface of the structure during tool operation is not predictable.
Second, the failure of diamond-impregnated structures has been linked to the presence of the randomly distributed diamond content. Historically, the random distribution of diamond content within the diamond-impregnated structure was viewed as desirable. The reason for this was that fresh cutting diamond was constantly being exposed on the working surface as the tungsten carbide matrix surrounding the diamond particles was worn away during the abrading, grinding, machining, or cutting process for which the structure was being used. However, areas of the structure with diamond clusters may lack sufficient matrix material to support diamond retention during tool operation, while areas of low or no diamond content tend to exhibit poor wear properties. The random diamond distribution further allows for an accompanying random distribution of matrix material striations trailing behind the exposed diamond particles. The striations reduce the ability of cooling fluids to carry heat away from the working surface, and the excess heat build-up at the working surface tends to accelerate diamond failure and wear of the tungsten carbide matrix.
Third, the inability to control diamond content with respect to the random distribution, with the resulting uneven diamond distribution across the working surface, necessitated the inclusion of extra diamond in the mixture so as to prevent occurrence of an uncut portion of the profile and subsequent “ring out.” This extra diamond has adverse affects on the tool both economically (in terms of added cost) and mechanically (due to a reduction in stress at the target interface by increasing the footprint in the same proportion, where stress is roughly expressed by the applied weight over the footprint area).
Fourth, if the fusing process utilized high heat, such as would be the case at least with respect to a sintering process, the applied heat could subject the diamond content to a graphitizing temperature for an unacceptable length of time. This would effectively degrade the properties of the impregnated diamond. The diamond-impregnated structure would then experience a reduced working life.
Fifth, the striations trailing behind the exposed diamond particles could produce a clogged interface between the structure and the surface of the target material (such as a rock formation in an earth drilling application). These striations further limit the depth of cut. Overall, this has an adverse affect on rate of penetration of the construct into the work target.
There is a need in the art for an improved drilling tool which addresses the foregoing, and other, problems experienced with the making and use of tools including randomly distributed impregnated diamond structures.